1. Field of the Invention
The subject invention relates to methods and apparatus for guiding a tape and, for instance, has utility in magnetic tape transports, photographic film handling apparatus and other tape or web transporting or handling equipment wherein precision guidance of a tape, film or other web is required or desired.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.45(a). No representation is hereby made that information thus disclosed in fact constitutes prior-art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material.
Throughout the years, many precision guiding techniques and apparatus have been proposed or implemented. By way of example, and not by way of limitation, precision guiding of a tape or web is important in information processing or handling equipment wherein a tape or web-shaped information carrier needs to be accurately positioned relative to information recording and playback devices.
Many proposed systems for the sidewise alignment of a longitudinally moving strip are not suitable in practice for most precision guidance purposes. For instance, the system disclosed in U.S. Pat. No. 3,243,089, by D. S. Cvacho et al., issued Mar. 29, 1966, employs a number of grooved wheels into which slanted rollers push a strip of material, such as employed in the manufacture of cylindrical metal containers. Such rugged handling of material would severely wear and damage most tape materials and would at any rate not afford the commonly requisite precision of guidance.
Another example of a past proposal unsuitable for present purposes may be seen in U.S. Pat. No. 3,536,239, by Grant F. Strong, issued Oct. 27, 1970. In particular, that proposal employs a pulley device for guiding and untwisting elastomer extrusions. To this end, Strong's pulley device has a base composed of tapered surfaces and bounded by convex sheaves or then by concave or inwardly slanted sides. In practice, such sheaves or sides would interfere with tape entry and exit, if such a pulley device were attempted to be employed as a tape guide.
The latter drawback would also attach to attempts to employ as tape guides slanted rollers with sheaves or sides extending at right angles to a cylindrical roller body, as shown, for instance, in U.S. Pat. No. 2,706,638, by H. H. Bruderlin et al, issued Apr. 19, 1955.
Several other proposals have attempted to realize tape transport or guiding systems with the aid of slanted or tapered rollers or guides, as may be seen from U.S. Pat. Nos. 3,967,788, 3,799,422, 3,494,525, 3,294,330, 3,143,270, 2,916,228, 2,894,702 and 2,862,715. The drawback of such systems customarily resides in an imposition of uneven stresses across the tape surface. For instance, the latter U.S. Pat. No. 2,862,715, by D. N. MacDonald, issued Dec. 2, 1958, proposes the use of several tape guides, each having a tapered body bounded by a reference surface extending at right angles to a longitudinal axis through the tapered body. The tapered body, which acts as a tape guide, imposes on the advancing tape a transverse force component by stressing the advancing tape unevenly across its major tape surface. In particular, that tapered guide stresses one edge of the advancing tape more than the other, thereby loading the tape against the straight reference shoulder provided at the base of the tapered body. This, in turn, has the drawback of prompting the tape to ride up or curl up on the reference shoulder, thereby adding further wear and tear to the wear and tear already occasioned by the uneven stresses imposed on the tape by the tapered guide.
A further type of web guide is apparent from U.S. Pat. No. 3,281,040, by F. F. Grant, issued Oct. 25, 1966. According to that proposal, a positive pressure gradient is established at the guiding element so that the moving web tends to slide "downhill" of the gradient and the edge of the web adjacent a guiding shoulder is brought into contact with that shoulder. Web guides of this type are useful in some applications but tend to be relatively long, bulky and air consumptive.
Further tape guide systems are apparent from U.S. Pat. No. 4,091,979, by L. B. Browder, issued May 30, 1978 to the subject assignee. While those systems afford a very high tape guiding precision, they would share with conventional approaches the disadvantage of tape curlup, if they employ a straight reference shoulder extending at right angles to the tape guiding surface. Such systems are further vulnerable to the effects of tape width variation or non-straightness of tape edges. Even with high-quality tape, variations of the order of 0.002/0.003 inches (50-75.mu.) are relatively frequent and result in a substantial variation of the force between the tape edge and adjacent reference shoulder, eventuating curling of the tape edge and climbing thereof onto the reference surface.